Yellow & purple nutsedge and the root-knot nematode

Weeds are often the most problematic to manage in and around agricultural fields. Yellow and purple nutsedge are difficult to manage and it seems brings an additional pest of concern. Nematodes! From Weed Science; Greenhouse experiments showed that yellow nutsedge established from root-knot nematode-infected tubers produced more tubers than noninfected tubers. Root-knot nematode populations became established on yellow nutsedge root systems when plants were established from tubers previously cultured with root-knot nematodes. When root-knot nematodes are present, yellow nutsedge tuber germination is not affected by metolachlor herbicide... the pests do not exist independently and that their management may be interrelated.

The nature of the symbiotic relationship between the nematode and the nutsedges is such that there is a positive correlation between the density of nutsedge plants in an area of a field and the level of concentration of the nematode. More nutsedges mean more nematodes.

An interesting video on this interaction can be viewed here: http://www.youtube.com/watch?v=E7ByJ3tFxDw

 

 

As the yellow and purple nutsedge is attacked by the root knot nematode the plant will increase production of the "nuts" or tubers. These tubers are the overwintering stage of the Yellow and Purple nutsedge plant. The root knot nematodes can use these tubers to survive in the winter as well. So the symbiotic relationship is that the nematodes will actually increase a Yellow and Purple nutsedge populations through increased tuber production, and the plants provide an overwintering (refuge) for the nematodes increasing their survival and population. In the end both populations increase hence the use of the symbiotic term.

Studies have shown that growing a nematode-resistant alfalfa (Medicago sativa L.) reduced nutsedge and nematode populations to nearly zero compared to nematode susceptible cotton (Gossypium hirsutum L.) which remained at damaging levels over 3 yr (with a subsequent rotation to a chile pepper (Capsicum annuum L.)). Nematode populations following the resistant alfalfa were comparable to populations after fumigation of cotton plots. The benefit of the alfalfa crop lasted for 1 yr; therefore, growers must consider long-term strategies for extending suppression of this pest complex.

Should you apply a nematacide when spraying for nutsedge? I would say that you should not. In order to better protect the efficacy of chemical products we need to be aware of resistance management.

Pest management for nematodes:

• Plants affected by plant-parasitic nematodes may be stunted and have pale or yellow-green foliage.
• Extracting and identifying nematodes from soil samples or infected plant material is the best means for determining if and which nematode species are responsible for poor growth. The mere presence of nematodes in a sample does not mean they are causing plant damage. The nematodes must be identified and quantified correctly to determine if management measures are needed.
• Soil fumigation before planting can be effective against nematodes, but fumigants are expensive and generally not economically for all crops.

Important to remember:

• Sanitation - Cleaning machinery, tools and clothing after working in a nematode-infested field often slows the spread of nematode species into other areas. Since nematodes reproduce on certain weed species, weed control can significantly help slow population increase.
• Use of nematode resistant plant varieties - Nematode resistant plant material is available for many crops. Resistant varieties are not damaged severely by nematode infection and can reduce nematode populations. Use of nematode resistant varieties in problem fields can be effective and the least expensive way to avoid losses. However, when resistant varieties are overused, new pathogenic strains or races of nematodes may appear.
• Crop rotation/cover crops - Crop rotation to a non-host crop can reduce nematode populations from reaching economically damaging levels. However, it is necessary to positively identify the species of nematode in order to know what plants are non-hosts.

Resources

• UC IPM Pest Note Nutsedges: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7432.html
• UC IPM Pest Management Guidelines Alfalfa Nematodes: http://www.ipm.ucdavis.edu/PMG/r1200111.html